You're certainly in a challenging situation there, an extreme example of something many of us go through. Both the responses you've received have elements I agree with. It seems to me that you need to convey to management that the current situation is not sustainable by anyone - they need to understand you are working beyond what is reasonable and this is not only unsustainable, it won't lead to the outcomes they hope for.
A big factor in this is that the company is undergoing a process of change for which they have little or no reference point. Steering a company into digital product development is hard, and they need to learn what is doable and what isn't. You're the one doing it, so they need to know from you what's right and wrong. In that, I agree with maryshaw's point. The hard thing for you is conveying that to them without sounding like you're just complaining for the sake of it.
That's where pasztor_david's point about an ally comes in. The move to digital producer development is likely being driven by one or more people towards the top of the company (I don't know how large the company is, but this applies to any size). You want to help them achieve their aims but you need to explain to the driver of the new policy in the company that the current process won't succeed without more human resources. If the company can't invest in that, then it needs to rethink its aims and how to achieve them.
If you can identify and enlighten one person who has an investment in your success - it could be your immediate superior, it could be senior management, it could be a board member (careful with that, though) - that you need support to carry out the program the company has in mind, it becomes their responsibility to bring that to management.
While it can seem daunting to put together a case, it doesn't have to be really complicated. My immediate reaction to your post was that it is obvious that having one person do four or five jobs does not make good business sense. If you present the issues in terms of a business case, and emphasise what CAN be achieved with proper resourcing (and it sounds to me like you are sufficiently self-aware, organised and committed to do this) then it makes it hard for the company to ignore your points. I think this is what maryshaw means by taking the emotion out of the issue.
At the same time, I'd say you should let your passion shine through. You care. That's not something the company wants to lose, and it's not something you should hide.
If push comes to shove, you can ask for a meeting with management that includes an advocate for you, someone who has gravitas and an industry understanding who can help you explain why the current situation is not sustainable. While our industry does not yet have a formal structure that provides that kind of support, there are people who can do this. I've done it myself, once in person and once by providing a written statement.
Ultimately, you do have to look after yourself. If the stress of this job is too much and the company won't support your needs, you do need to consider moving on. The very way you're approaching this makes you someone very employable. You have multiple skills, an understanding of what can and can't be done and a commitment to make things work. I'd hire you. But job-changing is a scary prospect and a last resort.
Give the company the chance to really understand what is and isn't working about your current situation. Give the management person most committed to the new policy what they need to understand and explain a more practical approach. Make sure your immediate superior is in on this, if at all possible. Be clear about what is going wrong, why and what you think can address the issue - clarity of analysis and suggesting solutions will help you come across as professional rather than just complaining.
And if it comes to the crunch, walk away knowing it's the company that failed, not you.